• Journal of the Korean Data and Information Science Society
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• v.8 no.1
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• pp.85-89
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• 1997

In this paper, we consider a random replacement model with minimal repair, which is a generalization of the random replacement model introduced Lee and Lee(1994). It is assumed that a system is minimally repaired when it fails and replaced only when the accumulated operating time of the system exceeds a threshold time by a supervisor who arrives at the system for inspection according to Poisson process. Assigning the corresponding cost to the system, we obtain the expected long-run average cost per unit time and find the optimum values of the threshold time and the supervisor's inspection rate which minimize the average cost.

• Journal of the Korean Statistical Society
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• v.30 no.1
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• pp.89-98
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• 2001

Brown and Proschan(1983) introduced a model for imperfect repair. At each failure of a device, with probability p, it is repaired completely or replaced with a new device(perfect repair), and with probability 1-p, it is returned to the functioning state, but it is only recovered to its condition just prior to failure(imperfect repair or minimal repair). In this paper, we limit the number of consecutive minimal repairs by n. We find some useful properties about $\mu$$_{k}$, the expected time between the k-th and the (k+1)-st repair under he assumption that only minimal repairs are performed. Then, we assign cost to each repair and find the value of n which minimized the long-run average cost for a fixed p under the condition that the life distribution F os the device is DMRL.L.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.11 no.17
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• pp.9-14
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• 1988

A (s, S) inventory policy is studied for a continuous inventory model in which lead times are dependent on the ordering quantity. The model assumes that at most one order is outstanding and demands occur in a compound poison process. The steady-state probability distributions of the inventory levels are derived so as to determine the long-run expected average cost. And the computational procedure is presented.

• Journal of the Korean Operations Research and Management Science Society
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• v.18 no.1
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• pp.119-126
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• 1993

We study a manufacturing process that is quite common in semiconductor wafer fabrication of semiconductor chip production. A machine is used to process a job consisting of J wafers. Each job requires a setup, and the i$_{th}$ setup for a job is sucessful with probability P$_{i}$. The setup is prone to failure, which results in the loss of expensive wafers. Therefore, a tiral run is first conducted on a small batch. If the set up is successful, the test is passed and the balance of the job can be processed. If the setup is unsuccessful, the exposed wafers are lost to scrap and the mask is realigned. The process then repeats on the balance of the job. We call this as send-ahead policy and consider general policies in which the number of wafers that are sent shead depend on the cost of the raw wafer, the sequence of success probabilities, and the balance of the job. We model this process and determine the expected number of good wafers per job,the expected time to process a job, and the long run average throughput. An algorithm to minimize the cost per good wafer subject to a demand constraint is provided.d.d.

• Journal of Korean Institute of Industrial Engineers
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• v.5 no.1
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• pp.59-66
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• 1979

The objective of this paper is to develop a stochastic inventory system model under the so-called continuous-review policy with a Poisson one-at-a-time demand process, iid customer inter-arrival times {Xi}, backorders allowed, and constant procurement lead time $\gamma$. The distributions of the so-called inventory position process {$IP_{(t-r)}$} and lead time demand process {$D_{(t-r,t)}$} are formulated in terms of cumulative demand by time t, {$N_t$}. Then, for the long-run expected average annual inventory cost expression, the "ensemble" average is estimated, where the cost variations for stock ordering, holding and backorders are considered stationary.

• Proceedings of the Korean Reliability Society Conference
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• 2000.04a
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• pp.63-70
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• 2000

Brown and Proschan(1983) introduced a model for imperfect repair. At each feilure of a device, with probability p, it is repaired completely or replaced with a new device(perfect repair), and with probability 1 - p, it is returned to the functioning state, but it is only recovered to its condition just prior to failure(imperfect repair or minimal repair). In this paper, we limit the number of consecutive minimal repairs by n. We find some useful properties about ${\mu}$$\_$k/, the expected time between the k-th and the (k + 1)-st repair under the assumption that only minimal repairs are performed. Then, we assign cost to each repair and find the value of n which minimizes the long-run average cost for a fixed p under the condition that distribution F of the device is DMRL.

• Journal of Korean Society for Quality Management
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• v.24 no.3
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• pp.31-36
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• 1996

A Markovian stochastic model for a system subject to random shocks is considered. Each shock arriving according to a Poisson process decreases the state of the system by a random amount. A repairman arrives at the system periodically for inspection and repairs the system only if the state is below a threshold. Costs are assigned to each inspection of the repairman, to each repair, and to the system being in bad states below the threshold. The expected long run average cost is obtained and compared with that of the random inspection introduced by Lee and Lee(1994).

• KDI Journal of Economic Policy
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• v.13 no.2
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• pp.3-19
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• 1991

This paper attempts to identify key determinants of long run movements of real M2 by using the Johansen procedure for estimating and testing cointegration relations. It turns out that the real M2 equation has been stable over the long run despite rapid changes in financial structure since 1975. Moreover, the real M2 equation can be reduced to a velocity equation with the opportunity cost variable, expected inflation less the weighted average rate paid on M2 deposits, being the key determinant. However, it does not work to use a market interest rate such as the yield on corporate bonds in place of expected inflation for calculation of the opportunity cost. In the U.S., a market interest rate can be used, but not in Korea. Presumably, two somewhat different reasonings can be used to explain this result. One is that the yield on corporate bonds may not adequately reflect the inflationary expectations due to regulations on movements in interest rates. The other is that M2 deposits are not readily substitutable with such assets as corporate bonds because of market segmentations, regulations, and so on. From the policymaker's point of view, this implies that the inflation rate is an important indicator of a policy response. On the other hand, policymakers do not regard movements of the yield on corporate bonds as an important policy indicator. Altogether, the role of interest rates has been quite limited in Korea because of incomplete interest rate liberalization, an underdeveloped financial system, implementation procedures of policy measures, and so on. The result that M2 velocity has a positive cointegration relation with expected inflation minus the average rate on M2 implies that frequent adjustments of the regulated rates on M2 will be necessary as market conditions change. As the expected inflation gets higher, M2 velocity will eventually increase, given that the rates on M2 do not change. This will cause higher inflation. If interest rates are liberalized, then increases in market interest rates will result in lagged increases in deposits rates on M2. However, in Korea a substantial portion of deposit rates are regulated and will not change without the authority's initiatives. A tight monetary policy will cause increases in a few market interest rates. But the market mechanism, upward pressure for interest rate adjustments, never reaches regulated deposit rates. Hence the overall effects of tight monetary policy diminish considerably, only causing distortions in the flow of funds. Therefore, frequent adjustments of deposit rates are necessary as market conditions such as inflationary expectations change. Then it becomes important for the policymaker to actively engage in adjusting regulated deposit rates, because the financial sector in Korea is not fully developed.